Field of the Invention
The present invention relates to a photoacoustic apparatus and an image processing method.
Description of the Related Art
One imaging technique for visualizing the inside of an object is photoacoustic imaging. With photoacoustic imaging, first, an object is irradiated with pulsed light generated from a light source. As the irradiation light is propagated and diffused inside the object and absorbed by a light absorber such as hemoglobin in blood, an acoustic wave (a photoacoustic wave) is generated due to a photoacoustic effect. A plurality of receiving elements arranged around the object receives the photoacoustic wave and outputs a reception signal (a photoacoustic signal). By having a processor analyze the photoacoustic signal and perform image reconstruction, image data (a photoacoustic image) representing an optical characteristic value regarding the inside of the object is obtained.
Due to many factors, a photoacoustic signal may contain noise that causes a decline in SN ratio. Performing image reconstruction using a signal with low SN ratio results in low quantitativity of optical characteristic information. US Patent Application Publication No. 2010/0049044 discloses a method of reducing noise by performing pulsed light irradiation and photoacoustic signal measurement a plurality of times and averaging the plurality of acquired photoacoustic signals. Furthermore, US Patent Application Publication No. 2010/0049044 discloses a method of acquiring an ultrasonic image whose position is associated with that of a photoacoustic image and tracking the ultrasonic image to estimate and correct a body motion of an object. Moreover, photoacoustic signals after body motion correction are averaged to produce a greater noise reduction effect.
When an object is irradiated with pulsed light, there is a limit to a range in which imaging can be performed with high quality based on photoacoustic signals. This range is referred to as a field of view (FOV). Therefore, when an imaging object region of an object is greater than a FOV, photoacoustic signals are obtained by moving an irradiation position of pulsed light and shifting the FOV in small increments. In addition, by averaging the respective photoacoustic signals in consideration of the amount of movement, imaging can be performed with high precision on a wide imaging object region. When the body motion estimation described in US Patent Application Publication No. 2010/0049044 is to be performed on data captured by moving an irradiation position in this manner, correction of positional displacement is time-sequentially performed for each adjacent FOV of the object.
Patent Literature 1: US Patent Application Publication No. 2010/0049044